Intrinsic Epigenetic Regulation of the D4Z4 Macrosatellite Repeat in a Transgenic Mouse Model for FSHD

Abstract

Facioscapulohumeral dystrophy (FSHD) is a progressive muscular dystrophy caused by decreased epigenetic repression of the D4Z4 macrosatellite repeats and ectopic expression of DUX4, a retrogene encoding a germline transcription factor encoded in each repeat. Unaffected individuals generally have more than 10 repeats arrayed in the subtelomeric region of chromosome 4, whereas the most common form of FSHD (FSHD1) is caused by a contraction of the array to fewer than 10 repeats, associated with decreased epigenetic repression and variegated expression of DUX4 in skeletal muscle. We have generated transgenic mice carrying D4Z4 arrays from an FSHD1 allele and from a control allele. These mice recapitulate important epigenetic and DUX4 expression attributes seen in patients and controls, respectively, including high DUX4 expression levels in the germline, (incomplete) epigenetic repression in somatic tissue, and FSHD–specific variegated DUX4 expression in sporadic muscle nuclei associated with D4Z4 chromatin relaxation. In addition we show that DUX4 is able to activate similar functional gene groups in mouse muscle cells as it does in human muscle cells. These transgenic mice therefore represent a valuable animal model for FSHD and will be a useful resource to study the molecular mechanisms underlying FSHD and to test new therapeutic intervention strategies.

DUX4 induces a transcriptome more characteristic of a less-differentiated cell state and inhibits myogenesis

“…1A). Skeletal muscle in both D4Z4-12.5 and FSHD1 D4Z4-2.5 mice successfully regenerated, consistent with our previous observations (Krom et al, 2013).…”

“…RV, retrovirus. skeletal muscle, but the transgenic model has no overt muscle pathology (Krom et al, 2013). Here, we show that DUX4 expression increases during muscle regeneration, being expressed by myoblasts, although overall, DUX4 levels remained low.…”

Facioscapulohumeral muscular dystrophy region gene 1 over-expression causes primary defects of myogenic stem cells

“…For this reason, the potential role of 4q35 gene overexpression in the disease has been investigated at the functional level. DUX4 transgenic mice do not show any obvious muscle phenotype, despite displaying a DUX4 expression pattern and an alteration of DUX4 target genes similar to FSHD patients (Krom et al, 2013). On the contrary, mice overexpressing FRG1 (FRG1 mice), selectively in the skeletal muscle, display reduced muscle size and develop a muscular dystrophy resembling FSHD (Gabellini et al, 2006).…”

Targeting mRNA for the treatment of facioscapulohumeral muscular dystrophy

“…However, DUX4 is not expressed in normal functioning somatic tissues such as well-differentiated muscles fibers. While DUX4 is expressed in early development, it is transcriptionally silenced during cellular differentiation of somatic tissues by CpG methylation of D4Z4 repeats (12). In early development, DUX4 may play a role in activating a stem-cell-like transcriptional pathway (10).…”

“…Namely, DUX4 transgenic mouse model has not been able to capture the full disease phenotype of FSHD. For instance, the D4Z4-2.5 mice have normal histology of the limb, grip strength and creatine kinase (12,17). The challenge in generating a proper animal model for FSHD stems from the fact that D4Z4 macrosatellite encoding DUX4 is unique to primates (80).…”